We have isolated cDNA clones that encode the processing of a-mannosidase II from the insect cell host for baculovirus infection, Sf9 cells. Degenerate oligonucleotide primers were used based on the conserved protein sequences among the Class II a-mannosidases in a PCR reaction containing a cDNA preparation from Sf9 cells. The cDNA PCR product generated in this way was used to isolate full-length cDNA clones encoding the enzyme. These full-length cDNA clones are presently being used to determine the structure and substrate specificity of this insect processing enzyme. These studies will eventually lead to an understanding of the role of this enzyme in the processing of oligosaccharides in insect cell hosts for baculovirus expression.